Influences of land use on leaf breakdown in southern Appalachian headwaterstreams: a multiple-scale analysis

Stream ecosystems can be strongly influenced by land use within watersheds. The extent of this influence may depend on the spatial distribution of dev eloped land and the scale at which it is evaluated. Effects of land-cover p atterns on leaf breakdown were studied in 8 southern Appalachian headwater streams. Using a GIS, land cover was evaluated at several spatial scales, i ncluding the watershed, riparian corridor, and subcorridors that extended u pstream in 200-m increments for 2 km. Breakdown rate for American sycamore (Plantanus occidentalis) leaf packs varied significantly among sites (k = 0 .0051-0.0180/d) but fell within the range reported in the literature for sy camore. Leaf breakdown rate increased at sites with high shredder density a nd biomass. Further, breakdown rate and shredder density and biomass were p ositively related to mean substrate particle size. Several instream variabl es were related to watershed-scale features, but leaf breakdown rate was no t related to land cover at the watershed scale. Leaf breakdown rate was inv ersely related to % nonforested land within riparian subcorridors of simila r to1 km. Results suggest that the distribution of shredders is critical to leaf processing in these streams. In some streams, increased sediment inpu ts resulting from agricultural activity or residential development in ripar ian corridors may limit the distribution of shredders and thus influence le af breakdown rates. Alternatively near-stream development may alter the qua lity of allochthonous inputs to streams, and thus indirectly influence the distribution of shredders and instream processing.